1. Field of the Invention
This invention relates to a method of growing single crystals of high quality silicon carbide (SIC) for use as a substrate wafer for producing blue light emitting diodes, electronic devices or the like, and more particularly to a method of growing single crystals of SiC by a sublimation recrystallization process on a seed crystal of a SiC single crystal.
2. Description of the Related Art
A SiC single crystal, being a material chemically stable and resistant to high temperatures and radiant rays, holds high hopes for application in environment-resistant semiconductor devices. Having a wide bandgap, SiC single crystals are currently being used as material for short-wavelength light emitting diodes. In fact, 6H-SiC has a bandgap of about 3.0 eV at room temperature, and is used as the material for blue light emitting diodes. For this reason, there has been a keenly felt need for better quality SiC single crystal ingots for the manufacture of high quality wafers to be used for applications mentioned above.
As a production process of SiC single crystals by sublimation recrystallization, the process disclosed in JP-B-63-57400 (by Siemens Actiengesellshaft, Federal Republic of Germany) has been known, in which process the crystal growth is carried out at a fixed temperature. According to this production method, however, there are high possibilities of an occurrence of black linear defects extending from the seed crystal and an interminglement of polytypes other than the desired 6H polytype, and a decrease of crystal quality was witnessed in the later stage of the crystal growth when the source material is running short.
It is disclosed in U.S. Pat. No. 4,866,005 and WO-A-89/04055 (Davis et al.) that the source material temperature is fixed or is increased as the source material decreases. This is aimed to obtain a large SiC crystal by having the low-temperature portion of the source material sublimate and thereby allowing the crystal to grow for a long time after the high-temperature portion of the source material runs short.